Our objective is to produce and detect chromosomal inversions by exposing sperm and spermatids to mutagens. We identify genetic and chromosomal locations of inversions and maintain them in homozygous stocks and specific strain backgrounds if possible. We are using inversions as tools in studies of consequences to inheritance reproductive performance and viability of heterozygous and homozygous carriers. Studies are also in progress on meiotic and pairing properties of inversions by themselves and in combination. An interchromosomal effect of recombination has been discovered and will be studied. As a product of the lethal test systems we have developed, we are studying several induced recessive lethals for heterozygous effects and characterizing them for developmental properties in homozygous state. With specifically designed inversion stocks, we will map these induced lethals, which have all proved to be complimentary. We have used two inversions simultaneously to produce inverted transpositions and will study the aneuploid consequences of transposition carriers. We have made progress in using inversions to assess the general frequency of mitotic recombination and plan to pursue this study. Because every inversion of a minimal size is detected by our method, we are using them as an unbiased set to study questions of randomness of breakpoints both with respect to bands and chromosomes.